This present application relates generally to the combustion systems in combustion or gas turbine engines (hereinafter “gas turbines”). More specifically, but not by way of limitation, the present application describes novel methods, systems, and apparatus related to the downstream or late injection of air and fuel in the combustion systems of gas turbines.
The efficiency of gas turbines has improved significantly over the past several decades as new technologies enable increases to engine size and higher operating temperatures. One technical basis that allowed higher operating temperatures was the introduction of new and innovative heat transfer technology for cooling components within the hot gas path. Additionally, new materials have enabled higher temperature capabilities within the combustor.
During this time frame, however, new standards were enacted that limit the levels at which certain pollutants may be emitted during engine operation. Specifically, the emission levels of NOx, CO and UHC, all of which are sensitive to the operating temperature of the engine, were more strictly regulated. Of those, the emission level of NOx is especially sensitive to increased emission levels at higher engine firing temperatures and, thus, became a significant limit as to how much temperatures could be increased. Because higher operating temperatures coincide with more efficient engines, this hindered advances in engine efficiency. In short, combustor operation became a significant limit on gas turbine operating efficiency.
As a result, one of the primary goals of advanced combustor design technologies became developing configurations that reduced combustor driven emission levels at these higher operating temperatures so that the engine could be fired at higher temperatures, and thus have a higher pressure ratio cycle and higher engine efficiency. Accordingly, as will be appreciated, novel combustion system designs that reduce emissions, particular that of NOx, and enable higher firing temperatures would be in great commercial demand.